دارة إلغاء التشويش (ثنائي حجز التشويش) .. كتاب التلفزيون الملون والعادي

8-5 - Noise Cancellation Circuit (Diode)
(noise cancellation):

Figure (8) - (8) This circuit works to reduce or eliminate the interference that may affect the circuit of the automatic control controller AGC - resulting from sparks of ignition sparks in the explosive engines of cars and others, as well as from electric motors with coals - and current cut-off devices and others. Because this jamming may be in the same time as the horizontal pulses on which the reserved AGC system is based
It is used in the noise canceling circuit (dual noise reservation) (1), whose work is as shown in the circuit diagram

The composite visual signal coming from the output of the image detector carries the synchronization pulses with a negative direction, and makes the diode source of the jammer D1 with a positive value, with the influence of the resistance R2 - and keeps the synchronization pulses with a value slightly above zero - and with the positive bias makes D1 in the state of full conduction, and prevents Jamming pulses with a large amplitude in passing - so D1 works as a short circuit that passes the composite image signals without change.

And when the jamming pulses appear with the image signal, and the amplitude of the jamming pulses is greater than the synchronization pulses, it will make the diode in the negative voltage region, and lead to cutting off D1 during the jamming pulses - so the diode works as an open circuit with a breaker that prevents and blocks the passage of the jamming pulses from the image amplifier.

Noise - Inverter circuit:
​It is a circuit in which the composite signal including the synchronization pulses is introduced by means of the CR2 diode anode in Figure 9. Since its reverse bias is (6.8 volts) and the voltage barrier is (0.5) volts, this makes the diode not connect except at a voltage of 6.8 + 0.5 = 7.3 volts, and since the value of the synchronization pulse is 7.5 volts, the difference 7.5 - 27.3 volts is not sufficient to make transistor 05 in a conductive state, because its voltage is zero: qult and the voltage (2), volts is not sufficient to pass the barrier (the base emitter), while the jamming pulse that exceeds (7) volts will cause the transistor to connect 05 as an inverter, and the jamming pulse will appear on the collector. This reversed jammer pulse cancels out the non-reverse pulse of the composite picture signal and this cancellation takes place at point A of the reserved AGC input and at point B of the synchronization interval